1 Field of the Invention
This invention relates generally to drive mechanisms for pedal powered vehicles such as bicycles and tricycles and more particularly to bicycle drive mechanisms of the chainless planetary type.
2. Description of the Prior Art
The most common multiple speed bicycle uses a chain and derailleur system. The chain requires periodic cleaning and oiling to prevent premature chain failure and must be removed from the rear sprocket to change the tire. Chain maintenance is particularly troublesome if the bicycle is ridden extensively on dirt roads and trails. Also, when the rider is bearing down hard on the pedals on a hill, the derailleur usually will not carry the chain to a lower gear. Consequently, with a chain/derailleur system, the cyclist must anticipate the terrain and shift gears before getting on a hill in a gear that is too high, since he may not then be able to shift to a lower gear. Further, all the gears of a conventional ten or twelve speed drive are not efficiently usable because of the angle the chain makes with the sprockets, and shifting is not done in a simple set sequence that is easily mastered. These problems are eliminated with the present invention, as will be seen.
The transmission described in U.S. Pat. No. 2,505,464 by Debuit is a chainless type, located on the axis of the front wheel concentric with the pedal drive shaft, but Debuit's transmission is not planetary, is mounted alongside the wheel hub rather than inside it, is limited in the number of gear ratios it makes available (four plus a direct drive option), and carries the pedal torque through single gear teeth requiring large-tooth gears to prevent early fatigue failure.